1. Field of the Invention
The present invention relates to manipulator apparatus, and more particularly to manipulator apparatus for supporting and orienting the test head of an automatic test system.
2. Description of Related Art
Manipulators are intended to enable the position in elevation, azimuth, and orientation of a heavy test head to be adjusted manually so that the test head can be engaged accurately with and docked to a device handler, which is a device that feeds the test head with electronic circuits to be tested.
Electronic test heads are heavy assemblies comprising a structure supporting and protecting a large number of driver and comparator circuits which are connected to an automatic test equipment by connection cables. Each integrated circuit to be tested is successively positioned on the test head from a device handler to which the head is docked. In general, such heads are organized in the form of approximately rectangular cases which can be carried via two stub axles fixed to two opposite sides of the case in a balanced condition since the weight of the head is distributed symmetrically about these stub axles.
Other electronic test heads which will be called here asymmetrical heads have a cylindrical case with a radially extending rigid arm, containing electrical connection cables and cooling hoses.
Known manipulator apparatus such as the one described in U.S. Pat. No. 4,589,815 (Smith) comprises a vertical column formed by a H-shaped beam. An arm assembly supporting the test head moves vertically on the vertical column. The arm assembly has two vertical axes which are needed to support the weight of the test head when the head is manually moved away from the vertical column. In the Smith manipulator, the arm assembly cannot be rotated by 360x about the vertical column. Moreover, the H-shaped beam is lengthy, since its top has to be higher than the maximum upper position of the test head. This requirement results in a heavy and bulky vertical column. A further disadvantage is the use of manually handled metallic weights which are needed to balance the weight of the test head. The metallic weights are not easy to handle and the balance cannot be adjusted continuously. Furthermore the arm assembly does not provide large horizontal displacements.
Other manipulator apparatus also described in the above-mentioned patent. One variation comprises a pressure operated counterbalancing means for vertically displacing and supporting the weight of the test head. These pressure operated means are complicated since they need a pump, a pressure regulator and preferably a damping system which have to be permanently in operation to keep a constant fluid pressure in order to balance the weight of the test head.